
#14052: Significant GHCi speed regression with :module and `let` in GHC 8.2.1 -------------------------------------+------------------------------------- Reporter: RyanGlScott | Owner: osa1 Type: bug | Status: new Priority: high | Milestone: 8.4.2 Component: GHCi | Version: 8.2.1-rc2 Resolution: | Keywords: Operating System: Unknown/Multiple | Architecture: Type of failure: Runtime | Unknown/Multiple performance bug | Test Case: Blocked By: | Blocking: Related Tickets: #11547 | Differential Rev(s): Wiki Page: | -------------------------------------+------------------------------------- Comment (by osa1): Here's an even simpler reproducer: just repeat this line a few thousand times in a .script file: {{{ let x = 1 :: Int }}} Then run {{{ $ time (echo ":quit" | ghci -ghci-script Example.script Foo.hs >/dev/null 2>&1) }}} Results: {{{ GHC 8.0.2 2000 repetitions: 1,04s GHC 8.0.2 4000 repetitions: 2,06s GHC 8.0.2 8000 repetitions: 4,02s GHC 8.2.2 2000 repetitions: 2,17s GHC 8.2.2 4000 repetitions: 6,31s GHC 8.2.2 8000 repetitions: 21,39s }}} Demonstrates that adding a new shadowing binding is a constant time operation in GHC 8.0.2, but it's not constant time in GHC 8.2.2. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/14052#comment:16 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler